Electrophotography is a method in which an electrostatic latent image is formed by charging a light-sensitive material and then imagewise exposing, and after development with a developer, the resulting toner image is transferred to a transferring paper and fixed to obtain a copied material. The light-sensitive material to be used in this electrophotographic method basically comprises an electrically conductive substrate and a light-sensitive layer laminated thereon. Amorphous silicon is known as a material constituting the light-sensitive layer, and in recent years, various attempts have been made to improve the amorphous silicon. A light-sensitive material using the amorphous silicon is produced by forming an amorphous film of silicon on the electrically conductive substrate through glow discharge decomposition of silane (SiH.sub.4), for example. In this material, a hydrogen atom is incorporated in the amorphous silicon film and, therefore, the material exhibits good photoconductivity. In the amorphous silicon light-sensitive material, the light-sensitive layer has features that a surface hardness is high, abrasion resistance is excellent, heat resistance is high, electrical stability is excellent, range of spectral sensitivity is broad, and light sensitivity is high; it has ideal properties as an electrophotographic light-sensitive material.
Although the amorphous silicon light-sensitive material has excellent characteristics as described above, it has disadvantages in that dark resistance is relatively low, and thus dark decay of the light-sensitive layer is large and even if the material is charged, no sufficiently high charged potential can be obtained. That is, the amorphous silicon light-sensitive material suffers from disadvantages that when the material is charged and imagewise exposed to from an electrostatic latent image, and then the latent image thus formed is developed, electric charges on the surface of the material are decayed until the imagewise exposure, or until the developing step, electric charges on areas where light is not irradiated are decayed and, as a result, necessary charged potential for development can be obtained only with difficulty.
The decay of the charged potential is greatly influenced by circumstances. Particularly under high temperature, high humidity circumstances, the charged potential is seriously decreased. Moreover in repeated use of the light-sensitive material, the charged potential is gradually decreased. In production of copies by the use of the electrophotographic light-sensitive material in which the dark decay of charged potential is large, there are obtained only such copies that an image density is low and reproductivity of intermediate tone is poor.
In order to overcome the above problems, a method has been proposed in which a photoconductive layer of amorphous silicon is formed, and on this layer, amorphous silicon carbide, amorphous silicon nitride, or amorphous silicon oxide, for example, is formed by a plasma CVD method, thereby providing a charge blocking layer which is also to act as a surface protective layer.
However, in the amorphous silicon light-sensitive material with the above surface layer provided thereon, image blur occurs by repeating a copying operation. This phenomenon occurs seriously particularly under high humidity conditions; thus the light-sensitive material cannot be used for the usual electrophotographic process.
Moreover, although the amorphous silicon produced by the plasma CVD (chemical vapor deposition) method has a high surface hardness, it is broken more easily than a selenium-based light-sensitive film or an organic light-sensitive film, and is poor in impact resistance. Thus the light-sensitive material using the amorphous silicon as a main component is scratched by a paper-peeling click, for example, in a copying machine and a printer; as a result, white or black spots are readily formed on copied images.
The amorphous silicon light-sensitive material has hemispheric defects with a diameter of 1 to 30 .mu.m on the surface of the light-sensitive layer. In repeating of the copying operation, electric or mechanical breakage occurs at the above defect parts, thereby producing white or black sports on the image and reducing the quality of the image.